188 Messrs. Hancock & Atthey on Anthracosaurus Russelli. 



sufficient to cause us to doubt the specific identity of the two 

 specimens in question. 



We must now turn to the character of tlie teeth themselves. 

 In our specimen they have the same irregularly rounded base 

 as those of the Scotch specimen ; and like them they are, 

 towards the apex, a little flattened, giving to the section of the 

 crown an elliptical contour, the long axis being in the direc- 

 tion of the jaw ; and on the frontal and dorsal aspects they 

 are slightly carinated. So far the teeth agree ; but Prof. 

 Huxley describes the surface of those in his specimen as 

 ridged, not grooved, while in ours they may be said to be both 

 grooved and, to some extent, ridged. The base of the teeth, 

 when in a good state of preservation, exhibits narrow, shallow 

 grooves, the interspaces being comparatively wide and usually 

 a little prominent, though sometimes almost flat. This dif- 

 ference in the two instances is, perhaps, of not much import- 

 ance, and may be accounted for by the peculiar state of pre- 

 servation of the specimens : we shall shortly endeavour to 

 show that this is the fact ; in the meantime we will say a few 

 words on the internal structure of the teeth. In this respect 

 there is also some slight difference ; our sections of the teeth 

 and those described by Prof. Huxley do not exactly agree. 

 The only diflerence of any consequence, however, can be ex- 

 plained, we think, by supposing that the sections were made 

 from different parts of the tooth. In Pteroplax^ the pulp- 

 cavity, near the root of the tooth, is radiated, as it is in An- 

 thracosaurus ; a little nearer the base the radial spaces are 

 wider, a little further up they are contracted, and still higher 

 up they are contracted more, and ultimately they are lost, and 

 the cylindrical form of the pulp-cavity established. We may 

 therefore presume that the sections described by Prof. Huxley 

 were made near to the base of the tooth in AnthracosauruSy 

 and consequently the radial form of the pulp-cavity was 

 strongly developed. Our sections are from higher up the 

 tooth ; and the result is, that the radiation of this cavity is very 

 imperfect and in part obliterated. In other respects the struc- 

 ture appears to agree witli Prof. Huxley's description : but 

 this observation applies only to the general arrangement of 

 the parts ; for, as the learned Professor remarks, " the details 

 could only be made intelligible by elaborate figures," and such 

 were not given. 



In Mr. Atthey's collection there is a portion of a right man- 

 dible which was obtained at NcAVsham, and which we ori- 

 ginally thought belonged to Fterojyiax, but which we now 

 have no doubt belongs to Anthracosaurus. The surface-sculp- 

 ture of the bone, the general form, character, and internal 



